Efforts have been made for a long time to produce pure, directly compressible forms of vitamin C and other vitamins on a commercial scale, although without great success. Most of the known commercially obtainable, direclty compressible vitamin forms contain at least 2% of adjuvants. The presence of the adjuvants aid the flowability and compressibility of the powders and the hardness, friability resistance, disintegration time and stability against decolorization of the compressed forms, e.g. tablets, including effervescent tablets, cores etc. The water insolubility, and thus, the sedimentation, of certain adjuvants during the dissolution of the vitamin in water is a great disadvantage.
A known method for the production of vitamin powders, which necessarily contain small amounts of adjuvants, comprises spray drying an aqueous suspension of the vitamin, for example, vitamin C, and the adjuvants such as carbohydrates and film-forming hydrophilic, organic colloidal materials, for example, gelatine, water-soluble casein derivatives, water-soluble resins or water-soluble cellulose derivatives. However, the thus-obtained powder is not directly compressible and must be mixed with a lubricant before it becomes a directly compressible form. Such a method is described, for example, in U.S. Pat. No. 3,293,132.
An additional method for the production of directly compressible vitamin powders is described in U.S. Pat. No. 3,396,226. In that patent, a vitamin C powder is prepared by mixing vitamin C and microcrystalline cellulose, in the presence of a lubricant, especially titanium dioxide or magnesium stearate, before it can be compressed into tablets and the like.
A further known method for the production of directly compressible vitamin powders is known from U.S. Pat. No. 4,533,674. Here, a vitamin C powder is prepared by spray drying an aqueous suspension of vitamin C and a binding agent, e.g. microcrystalline cellulose, in the presence of an absorbent, especially silicon dioxide. In this case also a lubricant, e.g. magnesium stearate, must be added to the thus-prepared vitamin powder before it can be compressed into tablets and the like.
Another method is described in PCT Application No. PCT/US 84/01694 (Publication No. WO 85/01877) in which the lubricant is not mixed subsequently with the vitamin powder, but is admixed during the spray drying process or is already present in the aqueous suspension which contains vitamin C, a binder, and a lubricant.
The above known methods are, however, rather complicated, as pre-mixing steps and in some instances also post-mixing steps are required. Further, immediately after spray drying, the methods lead to vitamin powders which necessarily contain a substantial amount of adjuvants. The present invention largely solves these problems and is a simplification of the production methods hitherto used.